Regeneration of caustic alkali solutions containing mercaptans



Patented July 31, 1956 United States Patent-m 2,157,074

free oxygen in the presence of an inorganic oxidation 2 7575074 catalystwhich essentially comprises the copper radicle. v p I I w I, g Theinvention is advantageously carried into effect by blowing themercaptan-containing caustic alkali solution with air in the presence ofa copper catalyst in a concen- John Raymond Grayson andCharle s EmlynE'vans,Lontration of between 0.00008% and 0.0008% (wt. cu./vol.). d011,England, asslgnors to The Bntlsh Petroleum m- The use of 0.00008% ofcopper as catalyst more than P y Limited I doubles the regeneration rateof uncatalysed solution .Nonrawingb Application February 9,1952, whilethe regeneration rate is-increased from between s l 70,90 4 to 5 timesby raising the copper concentration from 0.00008% to 0.0008%, but theincrease of the copper ims P m i RDh lQ Gr Bmam content beyond 0.0008%does not increase the regenera- Fehruary 14,1951 tion rateproportionally.

7 Cl i ((11; 23 -134) It has been found that the rate of regenerationfalls 15 with increasing concentration of the caustic alkali solu- This.invention relates to the; regeneration. of caustic lion until, in theCase of Caustic Soda, at a Concentration alkali solutions, which, havebeen used for the removal of Of about 15% NEOH/ 100 Sollltion) theremm-Qaptans f soul; h d b i1 is only a very small increase in theregeneration rate.

.It is. known that suchv mercaptan-containing caustic It has furtherbeen found that a PP catalyst is alkali solutions mayv regenerated b bli i h .20 eifective for the regeneration. of stronger caustic alkalioxygen Or an cxygen-c0ntaining gas in the presencg of an Solutionsprovided the Operation is carried Out ill the organic catalyst.Polyhydroxy benzene carboxylic acids PreSenCc 0f Solutizel' Solubility Pi. a :or tannins have been used commercially as'such oxidasubstancewhich increasesthe solubility of mercaptans in {ion patalysfs but inthis case is necessary for a small the SOlutlOIl. F01 example, the rateOf regeneraproportion of themercaptans tobeleftin theregenerated 5 i Ofa 16% Caustic Soda Solution Containing N caustic alkali sqiution i m toi i i h Oxidation sodium cresylate is considerably increased by acopperof the oxidation catalyst. In,.this. connection-,,it has also00110611081501} 0f P be nrprop se t ad to th Caustic alkalinsolutio anThe invent on Will be further described with reference extremely smallquantity .as low. .0001.%. of, a come to the fOllOWlllg eXPenmentS-pound of a metal selected from, the group consisting of caus ticsoda/mefcaptan Solutions were made P Y copper, nickel, cobalt and iron.Suchaddition isustated dlssolvlng mercaptans y 71%, methyl to. rendersuitable for use as oxidation;cata1ysts,.phenolic P PY ill 7% NaOH togive mercaptan iodill6 om ound -whichare. therwiseinefie tiye. 1 lyslightly values of approximately 300. 300 ml. of solution Were effectiveas such: catalysts. air blown at a rate of 12 cu. ft./hr. at atemperature of .It has now been discovered that. the; mgoneration; ofmercaptan-containing caustic alkalisolutions. may be In order todetermine the effect of copper concentraeffected without the use. of anorganic catalyst: but in tion, a copper sulphate solution was preparedcontaining he presence: If-.3111 inorganiescataly t.essentially com- 2.4gm. cu./litre. Varying quantifies were added to 300 prising the. copper.radicle, .which -is notgitself susceptible ml. of 7% soda/mercaptansolution as prepared above to oxidation with the: advantage; that theregeneration and the solutions were air blown as described above. The .of the caustic alkali solution-may; .be carriedrasnear cornresults areset out 'in Table I below.

7 Table 1 [300 mls. 7% soda/mercaptan solution. Airrate 12 cu. ft./hr.Temp. 8590 F.]

.Me rcap tan Iodine Value:

after 0 minutes after 15.minutes after KOminutes after minutes after'minutes after minutes.- after minutes.. after minutes after 1 20minutes. after minutes. after 240 minutes after 300 minutes. AverageIodine Value Dropper 15 mms pletion as possible. i The following TablesII and III show the eifect of vary- 7 According; to thea invention, the,regeneration of' a 70 ing the rate of air blowing and the sodaconcentration pgptanrcontainingg.callatic alkalinsplution is effectedrespectively, using 300 m1. of solution. containing 0.0008

by treating; said= so1ution,withmxygensoraa gas containing w./v. percentcopper.

Table 11 ./V.). NaOH/iOO mls. solution. 300 mls. Solueration, s olutizersolutionincreased by the addition of copper.

We claim:

1. A process for the regeneration of a mercaptancontaining causticalkali solution derived from a mer- Air Rate, wit/hr 7 12 25captain-containing oil by extracting the oil with a caustic alkalisolution to cause the mercaptan to pass thereinto 368 366 376 and thenseparating said mercaptan-containing caustic after minutes 320 310 290alkali solution from the oil for regeneration which procggg igfig ggi g8fig 1Q ess consists essentially of treating the mercaptan-containafter60 minutes 176 -3 112 ing caustic alkali solution with free oxygen inthe presaiter 75 minutes 136 106 48 after 90 Emmet" 70 42 14 ence solelyof an inorganic catalyst consisting essentially after 105 minutes 10 ofbetween about 0.00008% and 0.0008% of copper sulphate measured as weightof copper per volume.

Table III [300 mls soda/mercaptan solution. Air rate 12 cu. it./hr.

Temp. 8590 F.]

Total Alkalinity of Soln. (gins) NaOH/ 100 mls. soln 3. 2 3. 2 5. 2 5. 26. 8 7. 0 7. 0 10. 2 10. 2 11. 6 15 15 15 15 Copper Sulphate Soln. Aadded, mls Nil 1. 0 Nil 1.0 1.0 N11 1.0 Nil 1.0 1. 0 Nil 1. 0 5. 0 25. 0Copper Concentration percent (W./V.) 0. 0008 0. 0008 0. 0008 0. 0008 0.0008 0.0008 0. 0008 0.004 0.02

Mercaptan Iodine Value:

After 0 mins After 15 mins After mins After 45 mins.

minutes) 12 It will be seen from Table II that the rate of mercaptanremoval increases with increasing air rate. A drop in iodine value of192 took place in 60 minutes at an air rate of 7 cu. ft./hour and a dropof 264 in 60 minutes at 25 cu. ft./hour. It is clear from Table III thatthe weaker the soda solution, the greater is the rate of mercaptanremoval.

In order to demonstrate the effect of copper as a catalyst in theregeneration of solutizer solutions by air blowing, the followingexperiments were carried .out using the same materials and methods asbefore.

(1) Air blowing of 4N NaOH+mercaptans with and without the addition of0.0008 w./v. percent copper as copper sulphate.

(2) Air blowing of 4N NaOH-l-LZ N sodium cresylate with and withoutmercaptans and with and without the addition of 0.0008 w./v. percentcopper as copper sulphate.

The results are set out in Table IV below.

2. A process in accordance with claim 1 wherein a mercaptan-containingcaustic alkali solution after separation containing more than theequivalent of about 15 grams NaOH/ 100 ml. solution, and which includesa compound which increases the solubility of mercaptans in the causticalkali solution.

3. A process in accordance with claim 1 wherein the mercaptan-containingsolution is treated with the free oxygen at a temperature of about to F.

4. A process in accordance with claim 1 wherein a mercaptan-containingcaustic alkali solution after separation from the oil does not containmore than the equivalent of about 15 grams NaOH/ ml. solution.

5. A process in accordance with claim 4 wherein the compound added toincrease the solubility mercaptans in the caustic alkali solution issodium cresylate.

6. A process for the regeneration of a mercaptancontaining causticalkali solution derived from a mercaptan-containing oil by extractingthe oil with a caustic Table IV [300 mls. solution. Air rate 12 cu.tt./hr. Temp. 85-90" F.]

Solution Used 4 N NaOH 4 N NaOH+L2 N Sodium Cresylate CopperConcentration,

W./V. Percent Nil 0. 0008 Nil 0.0008 Nil 0.0008 Iodine Value of SodaSoln. without Mercaptans (Blank) Nil Nil 440 440 430 428 MereaptansAdded Added Added Added Nil Nil Mercap- Mercaptan tan Total IodineValue: I. V. V.

after 0 minutes 396 450 794 854 826 380 430 428 after 30 minutes. 430736 296 734 288 after 60 minutes 340 418 684 244 620 174 424 424 after90 minutes. 330 390 628 188 544 p 98 after minutes- 316 352 592 152 48034 430 420 after minutes 326 546 106 480 34 after minutes 288 300 502 62460 14 430 420 after 210 minutes. 470 30 It will be seen that theregeneration rate of 4N (16%) soda/mercaptan solution was increased butslightly by the addition of copper catalyst, while the rate ofregenalkali solution to cause the mercaptan to pass thereinto and thenseparating said mercaptan-containing caustic alkali solution from theoil for regeneration which process consists essentially of treating themercaptan-containing caustic alkali solution with gas containing freeoxygen in the presence solely of an inorganic catalyst consistingessentially of between about 0.00008% and 0.0008% of copper sulphatemeasured as weight of copper per volume.

7. A process for the regeneration of a mercaptancontaining causticalkali solution derived from a mercaptan-containing oil by extractingthe oil with a caustic alkali solution to cause the mercaptan to passthereinto and then separating said mercaptan-containing caustic alkalisolution from the oil for regeneration which process consistsessentially of treating the mercaptan-containing caustic alkali solutionwith air in the presence solely of an inorganic catalyst consistingessentially of between about 0.00008% and 0.0008% of copper sulphatemeasured as weight of copper per volume.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE REGENERATION OF A MERCAPTANCONTAINING CAUSTICALKALI SOLUTION DERIVED FROM A MERCAPTAN-CONTAINING OIL BY EXTRACTINGTHE OIL WITH A CAUSTIC ALKALI SOLUTION TO CAUSE THE MERCAPTAN TO PASSTHEREINTO AND THEN SEPARATING SAID MERCAPTAN-CONTAINING CAUSTIC ALKALISOLUTION FROM THE OIL FOR REGENERATION WHICH PROCESS CONSISTSESSENTAILLY OF TREATING THE MERCAPTAN-CONTAINING CAUSTIC ALKALI SOLUTIONWITH FREE OXYGEN IN THE PRESENCE SOLELY OF AN INORGANIC CATALYSTCONSISTING ESSENTIALLY OF BETWEEN ABOUT 0.00008% AND 0.0008% OF COPPERSULPHATE MEASURED AS WEIGHT OF COPPER PER VOLUME.